I thought I'd attach some photos of the door frame construction as it is so far.

Also, a photo of the extractor fan I've bought. It comes with a speed controller and I'm confident it's man enough.

How could I improve the isolation of my ventilation design? Beef up my silencer box by adding two layers of fire board green glued together on the exterior?

John

Your door frame looks ok, get some low density 75mm insulation batt and push some into the gap (Maybe 150mm in). You ideally needed to attach the fabric cover to the back of the door lining before it was attached. Is there still a gap between the lining and stud work where it was adjusted to fill, if so you might still be able to get some fabric behind it.

If not, I would ask your builder to do this:
Staple/nail some plastic membrane to the internal leaf stud work behind the lining all around the door, and stretch this across the cavity then staple/nail it to the blocks.
Fit the outer door frame (you said the door came with a frame if I remember right?). Set it forward in the blockwork so there is a lip to attach some timber to extend over the 75mm cavity but not quite touching the other door lining (5mm or so is fine), then caulk the gap.

*UPDATE* I just thought: just staple the plastic and then some fabric to the timber the door stop is attached to (after filling the cavity with insulation batt) and stretch them over to the concrete blocks then nail a thin piece of wood over the staples to finish it and make it look neat.

For the ventilation silencer, the problem isn't really the mass. You need to increase the insertion loss within the ductwork/silencer. This can be acheived by having more baffles (a second box) and multiple changes in duct size. The 150mm round duct might increase to 200mm x 200mm square within the first silencer then reduce back to 150mm round for the duct connecting to the second box which has 200mm square, finally exiting out of a diffuser with 300mm x 300mm free area.

*UPDATE* I just thought: just staple the plastic and then some fabric to the timber the door stop is attached to (after filling the cavity with insulation batt) and stretch them over to the concrete blocks then nail a thin piece of wood over the staples to finish it and make it look neat.

For the ventilation silencer, the problem isn't really the mass. You need to increase the insertion loss within the ductwork/silencer. This can be acheived by having more baffles (a second box) and multiple changes in duct size. The 150mm round duct might increase to 200mm x 200mm square within the first silencer then reduce back to 150mm round for the duct connecting to the second box which has 200mm square, finally exiting out of a diffuser with 300mm x 300mm free area.

Dan

Thanks for the suggestions Dan.

Regarding my silencer box, I'm going with the two internal ones first (one for the exhaust and the other for the in) on opposite sides of the room. There won't be space for any more inside the room. If necessary I can have another one outside for the passive inlet, but it'd be more problematic for the exhaust given the exterior fan I'm using (see photo). This fan is recommended for studios where the aim is to keep fan noise outside.

The company who supplied the fan advised 8-10m ductwork max, so I'm a little concerned about adding too much extra 'length' in the silencer boxes. Currently there are two 10m ducts snaked in the now inaccessible roof cavity. I've told my builder he'll need to pull some ducting out through the exterior holes that will be bored, and shorten the length, to allow for the silencer boxes. Am I correct in viewing the area in the silencer boxes as extra length for the fan (and passive air in) to travel through?

Finally, I want to put some fine mesh in to prevent insects getting in. The fan company suggest it shouldn't affect air flow significantly on this fan as long as this mesh is at the fan end. My builder has suggested putting it inside the fan unit just behind the vents. And likewise on the passive inlet vent.
Any thoughts here?

Regarding my silencer box, I'm going with the two internal ones first (one for the exhaust and the other for the in) on opposite sides of the room. There won't be space for any more inside the room. If necessary I can have another one outside for the passive inlet, but it'd be more problematic for the exhaust given the exterior fan I'm using (see photo). This fan is recommended for studios where the aim is to keep fan noise outside.

The company who supplied the fan advised 8-10m ductwork max, so I'm a little concerned about adding too much extra 'length' in the silencer boxes. Currently there are two 10m ducts snaked in the now inaccessible roof cavity. I've told my builder he'll need to pull some ducting out through the exterior holes that will be bored, and shorten the length, to allow for the silencer boxes. Am I correct in viewing the area in the silencer boxes as extra length for the fan (and passive air in) to travel through?

Finally, I want to put some fine mesh in to prevent insects getting in. The fan company suggest it shouldn't affect air flow significantly on this fan as long as this mesh is at the fan end. My builder has suggested putting it inside the fan unit just behind the vents. And likewise on the passive inlet vent.
Any thoughts here?

Thanks

John

Without adding silencers to both holes in the external leaf you are going to have problems I think. But you can see how you get on.

Ideally you would want your silencer closer to your fan. The silencer(s) does need accounting for as duct length.

The fan noise isnt your main problem here, it's your studio isolation. The drums wont be isolated as well as you want I think. The insect mesh is fine.

Can I ask what advice Wonks gave you? (Unless he asked you not to) but to be honest the flow looks severely restricted at each baffle. It's usually best to maintain the double cross sectional area throughout the silencer, or there might be bufetting etc. increasing air noise. In Rod's book his silencer example only slightly reduces the cross section at each turn. What cross section is your design at the 90degree turns?

Without adding silencers to both holes in the external leaf you are going to have problems I think. But you can see how you get on.

Ideally you would want your silencer closer to your fan. The silencer(s) does need accounting for as duct length.

The fan noise isnt your main problem here, it's your studio isolation. The drums wont be isolated as well as you want I think. The insect mesh is fine.

Can I ask what advice Wonks gave you? (Unless he asked you not to) but to be honest the flow looks severely restricted at each baffle. It's usually best to maintain the double cross sectional area throughout the silencer, or there might be bufetting etc. increasing air noise. In Rod's book his silencer example only slightly reduces the cross section at each turn. What cross section is your design at the 90degree turns?

Dan

Thanks Dan.

So the internal 'dividers' in my design are too long?

I've had a look at Rod's design and he has fewer compartments in his box than I'm suggesting. I always thought more (within reason) would work better?

Wonks kindly made some suggestions on another forum as per the photo attached.

The dividers aren't too long, the box is not deep enough. You need to increase the depth so the 200mm square cross section is maintained at the baffles too.

Having 4 baffles inside the box will increase isolation over 2 baffles yes.

Dan

Hi Dan

I found this diagram (Detailed Dimensions.pdf - attached) which a fellow poster said was supplied by Rod Gervais.

It's for a 250mm duct and, although the width of the entry and exit compartments are more than this (286mm), the measurement of the point where the air passes over the baffles is 155mm, and the width of the middle two compartments is 206mm.

Are you saying I need to maintain the 200mm even where the air passes the baffles - where I have circled in my other attachment? This is not like in the drawing from Rod.

I'm not the OP but I've run his wall design through a spreadsheet used at JLSayers and this wall design has the potential for a Transmission Loss of 70dB down to 40Hz.

I'm not sure on John's requirements but this is very high, and may not be necessary (especially considering the roof and especially the doorway will be VERY expensive and difficult to get near this.)

John, if you cant afford 65-70dB TL on your doors and roof then save money on your walls, drop the green glue and reduce to just a single layer of OSB and 1 layer of fireboard. This can still push 60dB.

I found this diagram (Detailed Dimensions.pdf - attached) which a fellow poster said was supplied by Rod Gervais.

It's for a 250mm duct and, although the width of the entry and exit compartments are more than this (286mm), the measurement of the point where the air passes over the baffles is 155mm, and the width of the middle two compartments is 206mm.

Are you saying I need to maintain the 200mm even where the air passes the baffles - where I have circled in my other attachment? This is not like in the drawing from Rod.

Thanks again.

John

Hi John,

Sorry about the delay. It's been a busy week.

Rod's design does seem to restrict flow, but in theory the 250mm round duct (49000mm2) would probably already have quite low velocity, so it first increases to 286mm x 286mm (82000mm2) then reducing it down would increase insertion loss.
It appears to reduce alot to 155mm x 286mm at the baffle, but in reality that's over 44000mm2, which is only 10% smaller than the original area. We then open back out to 206mm x 286mm (59000mm2) and at the exit to reduce the velocity again and hopefully be inaudible we increase to 286mm x 286mn (82000).

The restricted areas are only 10% less than standard flow for a tiny proportion of the silencer.

You could do something similar, but I suspect the velocity is a bit high for that with a 150mm round duct.

You might want to look over the comments to form your opinions on it's accuracy. (For the record, I believe the theory is correct, but almost impossible to achieve in practice without a huuuge budget for HVAC and doors)

Rod's design does seem to restrict flow, but in theory the 250mm round duct (49000mm2) would probably already have quite low velocity, so it first increases to 286mm x 286mm (82000mm2) then reducing it down would increase insertion loss.
It appears to reduce alot to 155mm x 286mm at the baffle, but in reality that's over 44000mm2, which is only 10% smaller than the original area. We then open back out to 206mm x 286mm (59000mm2) and at the exit to reduce the velocity again and hopefully be inaudible we increase to 286mm x 286mn (82000).

The restricted areas are only 10% less than standard flow for a tiny proportion of the silencer.

You could do something similar, but I suspect the velocity is a bit high for that with a 150mm round duct.

What velocity is the flow at your extractor?

Dan

Dan, no problem, I appreciate your latest response very much.

I've attached all the specs I have on the fan - it's the 150mm model.

I must admit I am struggling to come up with the exact design of the box. My builder is waiting for me to confirm in the next two days.

I've agreed with him that the top and one side of my boxes will be the inner ceiling and wall, which is made up of 2 layers of fire board with green glue between, a layer of 18mm OSB, and 100mm RW3 insulation behind.

So it will be the front side, bottom and end sides that are made and secured to the wall and ceiling, then caulked. These will be made of MDF with 2 layers of fire board green glued together (see second drawing attached).

But, as I say, the exact design - dims, lengths of baffles - is something I really could do with some help on.

I must admit I am struggling to come up with the exact design of the box. My builder is waiting for me to confirm in the next two days.

I've agreed with him that the top and one side of my boxes will be the inner ceiling and wall, which is made up of 2 layers of fire board with green glue between, a layer of 18mm OSB, and 100mm RW3 insulation behind.

So it will be the front side, bottom and end sides that are made and secured to the wall and ceiling, then caulked. These will be made of MDF with 2 layers of fire board green glued together (see second drawing attached).

But, as I say, the exact design - dims, lengths of baffles - is something I really could do with some help on.

thanks

John

It's ok to use the wall and ceiling as part of your silencer providing you can get a completely air tight seal when attaching it. Also some inner baffles will need to attach to the wall, so you could use brackets to screw them to the wall before caulking and attaching the final mdf face.

I find them easier to build on the floor though in mdf as a complete box and then beef them up once attached to the wall.

Rod recommends as close to (0.51m/s) 100FPM as you can get but definitely under 300FPM (1.52m/s).

Have you already bought the fan or can you get the size up and run it slower?

Do you need to run the fan at full speed? (To maintain more than 6 room volume changes per hour)

If so you'll need to drastically increase the duct size in your silencer to slow the air velocity and make it quieter. If you don't you'll hear the air rushing in through your inlet and sucking out of the extract.

To get 600m3/he under control your diffuser(s) will need a free area of around 0.16m2, 400mm square would get that. (Some diffusers only have 50% free area of their face size so you'll have to check though.

So your first and last sections of your silencer should be 400mm in width and 400 height or rectangular with an area of 16000mm2 or there about. You could reduce this to 200mm x 400mm at the baffles and the middle sections open out to 250mm x 400mm.

They wouldn't need to be this big obviously if you don't need 600m3/hr and can reduce the speed.

Dan

Ps. Budding studio builders out there, if your studio is big enough to need 600m3/hr, consider running silencers to 2 separate diffusers for inlet on opposite walls, as the diffusers won't throw very far with the reduced velocity we require and you'll get hot/cold spots in your room.

Even quarter speed is too high for him. I just checked John's room dimensions.
It has a volume of almost 38m3. So 228m3/hr is necessary (6 volume changes). So lets go 300m3/hr. He can run his current fan at half speed to get that which will reduce noise too.

At 300m3/hr John I would make your silencer first and last sections 300mm width x 300mm height and use a diffuser/grille with 0.1m2 free area. At the baffles reduce to 175mm x 300mm. middle sections can open out to 200mm x 300mm. Make each baffle around 300mm long. Remember to add on 50mm to all of these dimensions to account for your lining foam.

Even quarter speed is too high for him. I just checked John's room dimensions.
It has a volume of almost 38m3. So 228m3/hr is necessary (6 volume changes). So lets go 300m3/hr. He can run his current fan at half speed to get that which will reduce noise too.

At 300m3/hr John I would make your silencer first and last sections 300mm width x 300mm height and use a diffuser/grille with 0.1m2 free area. At the baffles reduce to 175mm x 300mm. middle sections can open out to 200mm x 300mm. Make each baffle around 300mm long. Remember to add on 50mm to all of these dimensions to account for your lining foam.

At the exit the flow should then be under 1m/s (200FPM).

Dan

Thanks again Dan - and also Nick.

I've already bought this fan and also bought a controller that the supplier recommended, for controlling the speed (see attached).

I appreciate your suggested dimensions Dan, and tips on mounting the boxes.

Even quarter speed is too high for him. I just checked John's room dimensions.
It has a volume of almost 38m3. So 228m3/hr is necessary (6 volume changes). So lets go 300m3/hr. He can run his current fan at half speed to get that which will reduce noise too.

At 300m3/hr John I would make your silencer first and last sections 300mm width x 300mm height and use a diffuser/grille with 0.1m2 free area. At the baffles reduce to 175mm x 300mm. middle sections can open out to 200mm x 300mm. Make each baffle around 300mm long. Remember to add on 50mm to all of these dimensions to account for your lining foam.

At the exit the flow should then be under 1m/s (200FPM).

Dan

Hi again Dan

I've attached a drawing which I've revised based on your suggested measurements (again scaling is a little out!)

Think I've got it right.. wasn't sure about your advice to make the baffles 300mm long.

I've attached a drawing which I've revised based on your suggested measurements (again scaling is a little out!)

Think I've got it right.. wasn't sure about your advice to make the baffles 300mm long.

I'd appreciate your comments. Nearly there I hope!

Thanks

John

You're almost there John. You need to think in 3D.

Look again at Rod's design and consider it a bird's-eye view. You may find it easier to design this way instead of side view.

Draw a circle to represent your inlet at the top right of your box (as opposed to Rod's side entry).

You need to measure 300mm from the inside edge at the top, down the right side. This is the inside edge of your first baffle. Draw this baffle as a 300mm line going left, the thickness of your baffles (including foam.) Measure from the tip of this line 175mm further left. This is the left inside edge of your silencer. The 175mm you measured is empty space for air to travel. Now measure from the bottom edge of the first baffle another 200mm going down the page. This is your second baffle. This goes from the left inside edge and extends 300mm right. You'll find it stops 175mm from the other side of the box.
Repeat the last step another 200mm down on the right side.
Then again 200mm on the left side.

Finally measure 300mm from the bottom of the last baffle. This is the inside bottom edge of the silencer. Draw a square/circle the size of your diffuser/grille that has a free area of at least 0.1m2, near the bottom left of your box for outlet.

The height of the box is 300mm. The baffles are the full height of the box.

The internal dimensions of the box will be (including the 25mm duct liner and assuming 25mm mdf for each baffle):
525mm x 1600mm x 350mm

Look again at Rod's design and consider it a bird's-eye view. You may find it easier to design this way instead of side view.

Draw a circle to represent your inlet at the top right of your box (as opposed to Rod's side entry).

You need to measure 300mm from the inside edge at the top, down the right side. This is the inside edge of your first baffle. Draw this baffle as a 300mm line going left, the thickness of your baffles (including foam.) Measure from the tip of this line 175mm further left. This is the left inside edge of your silencer. The 175mm you measured is empty space for air to travel. Now measure from the bottom edge of the first baffle another 200mm going down the page. This is your second baffle. This goes from the left inside edge and extends 300mm right. You'll find it stops 175mm from the other side of the box.
Repeat the last step another 200mm down on the right side.
Then again 200mm on the left side.

Finally measure 300mm from the bottom of the last baffle. This is the inside bottom edge of the silencer. Draw a square/circle the size of your diffuser/grille that has a free area of at least 0.1m2, near the bottom left of your box for outlet.

The height of the box is 300mm. The baffles are the full height of the box.

The internal dimensions of the box will be (including the 25mm duct liner and assuming 25mm mdf for each baffle):
525mm x 1600mm x 350mm

I'm a little concerned about the amount of space two boxes of this size will take up in my room.

Is the larger size needed because of the velocity of the fan, rather than required to lessen the sound of my music making it to the outside world?

If I can control my fan and run it at lower speed, would a slightly smaller box following your design, still reduce the sound I make going outside?

John

You're pretty much right there. I already calculated with running your fan at half speed and this reduced the size of the box to what I showed you (you can't reduce your fan much more safely though). You could go smaller still though yes, you will get a louder ventilation system though. If you reduce the area of each section by a third you will be just under 1.4m/s at the grille. Calculate each section like this: 300mm2 is 90000mm. A third of 90000 is around 60000. Square route of 60000mm is 244.95mm.

So go with 245mm x 245mm for your 300mm x 30mmm sections. Now you have a new height (245mm) do the same for the other sections. Example: 175mm x 300mm = 52500. Reduce by a third: 52500 * 0.67 = 35175. Find the new width: 35175 / 245 (your new height) = 143.75mm. So go with 145mm x 245mm for that section.

The isolation will probably not change much. The same amount of mass is in the way, just closer together.

You're pretty much right there. I already calculated with running your fan at half speed and this reduced the size of the box to what I showed you (you can't reduce your fan much more safely though). You could go smaller still though yes, you will get a louder ventilation system though. If you reduce the area of each section by a third you will be just under 1.4m/s at the grille. Calculate each section like this: 300mm2 is 90000mm. A third of 90000 is around 60000. Square route of 60000mm is 244.95mm.

So go with 245mm x 245mm for your 300mm x 30mmm sections. Now you have a new height (245mm) do the same for the other sections. Example: 175mm x 300mm = 52500. Reduce by a third: 52500 * 0.67 = 35175. Find the new width: 35175 / 245 (your new height) = 143.75mm. So go with 145mm x 245mm for that section.

The isolation will probably not change much. The same amount of mass is in the way, just closer together.

Dan

Thanks Dan. I appreciate all your help with this.

On another issue, I think I may have made a mistake with my electrician. He has started work installing my power sockets and lights.

I'm having two spotlight bars on the ceiling and I suspect I have asked him to mount one of them exactly where I ought to be looking to have an acoustic ceiling cloud.

Some photos are attached.

I plan to have my desk and speakers close to the end wall shown.

Do you think I could position a cloud around this light or should I ideally move it down the room?

On another issue, I think I may have made a mistake with my electrician. He has started work installing my power sockets and lights.

I'm having two spotlight bars on the ceiling and I suspect I have asked him to mount one of them exactly where I ought to be looking to have an acoustic ceiling cloud.

Some photos are attached.

I plan to have my desk and speakers close to the end wall shown.

Do you think I could position a cloud around this light or should I ideally move it down the room?

John

No prob glad to help, I've received tons of advice over at JohnLSayers that has filled in a lot of empty spaces in my knowledge. So it feels good to pass on what I can.

Is your cloud going to be soft at this point (ie absorption)? If so, I would build a frame for it with a piece of timber running along the center line and mount the light bar on the cloud itself screwed to this timber.

No prob glad to help, I've received tons of advice over at JohnLSayers that has filled in a lot of empty spaces in my knowledge. So it feels good to pass on what I can.

Is your cloud going to be soft at this point (ie absorption)? If so, I would build a frame for it with a piece of timber running along the center line and mount the light bar on the cloud itself screwed to this timber.

Dan

Thanks again Dan. The lights are fitted and it may be that I will just have to position my cloud up to them. If the recommended position is between speakers and listening point I think there's enough space.

Apart from coming back in the New Year for some finishing touches (including making my baffle boxes), my builder is done.

I did some initial testing and it looks like I'm getting around 48 dB reduction right outside my closed doors (although I appreciate a real test will be when I get a drummer in here).

However, I'm quite pleased so far as that's without any baffle boxes (I have open ducting) and more importantly, inadequate seals on my inner door in particular.

The exterior solid composite door appears to be performing very well, but the seals on the inner fire door are woefully inadequate. To be fair, I expected I would have to do some work on these so I'm not surprised.

I wonder if you could give me your thoughts based on the attached photos?

Currently, there's a brush seal (that came with the fire door) on the top and sides of the door frame. And inside that there's a cheap rubber draught exclude on all sides, which as you can see is already coming off.

I was wondering about getting a retro fit surface mounted automatic drop down seal for the bottom. Currently the gap between the door and the laminate floor is a whopping 19mm, so this will need to be reduced by a timber strip and/or threshold plate I guess. The height of the timber floor in the gap between the two doors, which my fire door closes to, is 42mm.